My name is Austin Bell. I am a graduate research assistant at the University of Minnesota, and this is a hands-on activity
demonstration of how to calculate exposure and dose. I developed this activity along with Peter Raynor at the University of Minnesota,
and along with the help of students at Dakota County Technical College.
For this activity you will need bubble wands, bubble solution, calculators, a tape measure, and a timer.
Learners also have the option of using their cell phones.
The first half of this activity deals with determining exposure concentration.
Exposure is generally defined as an agent’s contact with the outer part of the body.
Exposure concentration is defined by Sexton et al. as the concentration of an agent in a carrier medium, such as air or water.
As a class, learners should determine the volume of air in the classroom.
In order to do this, learners will need to measure the length, width, and height of the room.
If a room is irregularly shaped it is all right to simplify the measurements by assuming the room is like a box.
After the measurements are taken, the volume of the room can be calculated using the equation: Volume = Length x Width x Height.
In our example, the length of the room was 30 feet, the width of the room was 25 feet, and the height was 20 feet.
This gives us a volume of 15,000 cubic feet.
In exposure and dose calculations, however, we typically use metric units.
In order to change our results to metric units, we simply have to do a unit conversion. There are 35.3147 cubic feet in one cubic meter.
Therefore, if we divide our volume of 15,000 cubic feet by 35.3147 cubic feet, we end up with 420 cubic meters.
In the next step, learners should split into pairs throughout the room with one member of each pair responsible for blowing bubbles,
while the other is responsible for counting them.
Each individual should count and record the number of bubbles blown by his or her partner during one full breath.
They can do this either by using a phone or by keeping track in their head.
After one full breath has been counted, the pair should switch roles and repeat the previous step.
These different sampling methods have their advantages and disadvantages that are not unlike actual sampling methods.
For example, keeping track of the bubbles on your own gives you a clearer picture over time to how many bubbles were blown,
but there is the possibility that the individual may miss a few bubbles.
On the other hand, taking pictures with your phone will capture all of the bubbles, but is only a snapshot in time.
Each pair should average their individual bubble counts to create a group average.
For example, let’s say the first person in the group counted 30 bubbles and the second person in the group recorded 42 bubbles.
You would then add these two counts together and divide by two in order to get your group average, which in this case is 36 bubbles. 0:03:28.033,0:03:28.000
Each pair should record their average bubble on a list along with their classmates.
The class should then aggregate all of the pair averages into a class total.
In our example, the first group had an average of 36 and the other groups followed for a class total of 223 bubbles.
You can then determine the classroom concentration of bubbles by dividing the
total number of bubbles by the volume of the classroom.
For our example, we had 223 total bubbles which would then be divided by our classroom volume of 420 cubic meters.
This gives us a classroom concentration of 0.53.
The second half of the activity deals with dose, dose rate, and cumulative exposure.
Dose is defined as the amount of the agent that is actually ingested, inhaled, or applied to the skin.
Learners should pair off into the same groups from the first half of the activity.
In these pairs one person should blow bubbles while the other pops them.
The person popping bubbles should keep track of the amount that they pop. Learners should do this for a couple of minutes.
In our example we recorded the bubbles popped during a 2 minute interval.
After one person is done popping bubbles, the pairs should switch roles and repeat this step.
The individual dose is the number of bubbles someone pops, for example 50.
The individual dose should not be averaged across pairs because dose is very specific to the person that is subjected to it.
In order to get an individual dose rate, you need to divide the dose, in our case the total number
of bubbles popped, by the length of time in which the popping took place.
In our example if someone had a dose of 50 bubbles over a two minute time period,
they would have a dose rate of 25 bubbles per minute.
Cumulative Exposure is determined by multiplying the exposure concentration by the duration of the exposure.
In our example, the exposure concentration was 0.53 bubbles per cubic meter,
and our duration of exposure, the length of time the bubbles were popped was 2 minutes.
This gives us a cumulative exposure of 1.06 bubble-minutes per cubic meter.
The main point of this activity is to highlight the differences between exposure and dose.
Exposure is an agent that people are exposed to but does not necessarily enter their body,
while dose is the amount of an agent that actually comes within the body.
Other things to think about are what factors affect the exposure and dose, for example, the room volume,
the amount of time sampled, and the amount of bubbles in the room during this time.
Hopefully this video made this activity a little clearer. Thank you for watching.